Field of the Invention
This invention pertains to innovative structures for tensioning arrays of solar photovoltaic (PV) cells, solar sails, and antenna elements that have been folded into compact shapes using principles of origami, for satellite and spacecraft applications, as well as terrestrial applications.
Introduction and Related Art
Recently, a variety of researchers have investigated origami and folding techniques for their value in efficiently packing large deployable space structures. For example, the Air Force Research Laboratory (AFRL) has been investigating and developing foldable membranes and arrays [1,2], retractable solar sails [3], foldable parabolic surfaces [4], and spiral-wrapped reflectors with a flexible laminate gore concept [5]. Another relevant example is from the Japan Aerospace Exploration Agency (JAXA) and their IKAROS experimental spacecraft, a 20-meter spinning solar sail. The folding pattern for the sail was relatively simple, consisting of an accordion fold of each quadrant of the sail, which is then wrapped around a central hub. Thickness-accumulation effects in the 7.5 micron sail material was significant enough that the wrapping and the management of the unfolding had to be carefully engineered to prevent tearing or binding of the sail material [6].
Most deployable space structures utilizing origami techniques have varying degrees of success and equal share of developmental challenges. Often, engineering resources are heavily invested into lowering the risks in stowage and deployment of these structures, as in mitigating tearing and binding, synchronizing a complex deployment with several degrees of freedom, managing potential bifurcation of certain areas of a structure, and maintaining structural efficiency when having to make technical trades.
The packaging and deployment of membranes and flat arrays, such as solar sails and solar arrays, is often a topic of research in deployable space structures. Thickness accumulation effects of fold patterns can create unexpected complications with packaging. For example, the two-directional Z-folding pattern, which has a perfect packaging efficiency if the fold regions are discounted, is based on an accordion fold, where it is first accordion folded in one direction, and then in the perpendicular direction. The secondary fold can often be problematic, as each fold must span the entire thickness of the first accordion fold [7].
An AFRL experiment [8,9] on studying tensioned precision structures (TPS) developed a folding pattern to have a perfect packaging efficiency (in a square shape) and cancelled-out thickness accumulation effects. FIGS. 1-7 show the sequential deployment of a 1/100th scale model of the helical triangular folding pattern of the 5 m×2 m tensioned TPS array 8, which folds and stows to a 1 m by 1 m stack 8′. When folded, each set of fold edges and panels along the length of the TPS array exist in their own plane perpendicular to the stacked pattern direction and they never coincide, which effectively cancels any interaction between panel thickness and the folding pattern. A drawback of TPS folding pattern 12 is its helical twisting behavior when being unfolded, and non-deterministic deployment process, which may not be simple to deal with when deploying a space structure, for example. For terrestrial applications, this twisting behavior may not be a problem.
The AFRL TPS folding pattern 12 was discovered to be a spiral sub-pattern of a global folding pattern [10]. The global pattern folds with the same thickness canceling properties, but closes into a cylinder. If allowed to intersect, the global folding pattern continues to collapse into a stacked square package. The TPS pattern 12 is rotated 45 degrees from the Structural Origami ARray (SOAR) pattern 10. Both the AFRL TPS helical sub-pattern and the SOAR pattern collapse into a cylinder, and then into a square with no self-intersections. The alternative SOAR pattern 10 is torsion-free during deployment, which makes the deployment process deterministic in both directions.
Both of these rectangular sub-patterns (TPS and SOAR) are limited in extent only by their respective unfolded widths, and they may fold in arbitrary length. FIG. 2 show sequential perspective views of the unfolding sequence of a folded package comprising a SOAR triangular folding pattern 10 with 3 repeating units (N=3), perfect packaging efficiency, and deterministic, non-helical deployment.
One difficulty with the TPS and SOAR triangular folding patterns is that each fold vertex has three degrees of freedom, which results in a “floppy” (not fully controlled) structure throughout folding and unfolding. If the sequence is altered by simply using trapezoids in place of triangles, this reduces the folding pattern to one degree of freedom (DOF) at each fold vertex, and the fold structure exhibits a synchronized, deterministic folding behavior from stowed to fully deployed.
For small satellite program managers and integrators, who must contend with increasing power consumption of small spacecraft with advanced electric propulsion and/or science instrumentation, the SOAR system is an extremely high performance, deployable solar array system that delivers high power output and exceeds state-of-the-art packaging efficiencies. Unlike existing Z-folding panel or rolled architectures, this approach utilizes a two-dimensional packaging scheme of the flexible blanket/substrate that is coupled with a simple and compact supporting structure that stabilizes the array (tension/compression columns or internal lattice structure). This enables large deployed areas populated with high efficiency photovoltaic (PV) cells or antenna elements, which compactly stows in a square form factor with thin stack height, and minimizes impingement on spacecraft bus internal volume.
Patents have been issued relating to foldable arrays of solar panels for spacecraft using traditional accordion or Z-folding patterns, including: U.S. Pat. Nos. 4,880,188; 5,131,955; 5,520,747; 6,423,895; 6,478,261; 6,609,683; 6,637,702; 7,211,722; 8,616,502; and 9,444,394. Patents and applications have been issued/published relating to origami folding patterns for solar arrays, solar sails, and parabolic antennas, including: U.S. Pat. Nos. 8,356,774; 8,384,613; 9,496,436; 9,214,722; 2008/0223431; 2014/0001247; U.S. Pat. Nos. 5,296,044; 8,462,078; 8,462,078; and 9,156,568. Patents have been issued/published for large-strain fiber-reinforced composite hinges, including: U.S. Pat. Nos. 5,239,793; 6,321,503; 6,343,442; 6,374,565; 7,354,033; 8,074,324; 7,365,266; 7,895,795; 2015/0131237; and 8,434,196.
Against this background, the present invention was developed.